US2866144A

US2866144A - Commutatorless converter motor with

Info

Publication number: US2866144A
Authority: US
Publication date: 1958-12-23
Anticipated expiration: 1975-12-23

Description

Dec. 23, 1958 E, KERN COMMUTATORLESS CONVERTER MOTOR WITH SUPPLEMENTARY WINDING Filed Jan. 25, 1956 United States Patent COMMUTATORLESS CNVERTER MOTOR WITH SUPPLEMENTARY WINDIN G Erwin Kern, Ennetbaden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company It is known in connection with electric motors to use a current converter instead of a commutator for producing a rotating field, the correct voltage always being supplied to the motor with the aid of a grid control system. For this purpose motors are used whose rotor is fed by way of this converter arrangement from a direct-current or alternating current system, the field being supplied with direct current either from a direct current network or by way of rectitiers from an alternating current system. It is immaterial whether the stator represents the armature or excitation circuit or the rotor the excitation or armature circuit.

When the supply comes from the direct current system the converters operate as inverters. When the supply comes from the alternating current network the motor is connected by means of rectiers and inverters, with or without an intermediate direct-current circuit. The use of inverters requires that special attention should be paid to the commutation process. lt is known that this should occur some time before the point of intersection of the consecutive alternating voltages which overlap. Premature ignition is necessary. This is the time between the occurrence of the ignition of the converter which takes over up to the instant when the point of intersection of the two consecutive voltages which relieve each other is reached, in this case the back voltages of the motor. It is known that it can be considered as consisting of two parts, the actual commutating time during which both converters are current conductive, and the free time which is necessary in order to attain aA complete blocking effect. With converter controlled motors both the commutation time and the instant when consecutive voltages relieve each other, depend upon the load, the commutation time increasing with the load, so that the ignition must be made to occur so early that the motor still operates correctly with maximum load and no short circuits between the voltages or unstable running occurs. The instant of the voltage change-over is made to occur earlier in dependence on the load. This makes an even earlier ignition necessary or if the ignition point is fixed, the load capacity of the motor is reduced. The displacement of the point of intersection of the opposing voltages which overlap, is known to be due to the effect of the armature on the excitation. At no-load, the eld curve has the form of a rectangle or trapezoid. With a load, however, the field curve becomes distorted by the armature reaction and at the same time displaced tangentially, so that premature ignition is reduced. This results in the aforementioned disadvantages.

According to the invention these disadvantages are eliminated by providing in the excitation part of the motor in addition to the excitation winding an additional winding which is supplied with a direct current proportional to the load current and whose magnetic axis is displaced with respect to that of the main held, so that its field opposes the armature reaction caused by the load. it is known per se to provide additional windings in'converter controlled motors. Up to the present these FGVice have only been employed to make the characteristic' curves of the motor dependent on the load. The field of such an additional winding thus always lies in the axis of the main field and does not inuence the ignition instant in the manner required when a converter feeds the motor. According to the invention the axis of the additional winding is displaced in the excitation circuit with respect to that of the main eld, so that the point of intersection of consecutive voltages can be intiuenced. The armature reaction can thus be completely compensated by the field of this additional winding, but it is also possible to make the field of the additional voltage so strong that the aforementioned intersection of the voltages is moved back as regards time and the displacement of the ignition in the leading sense is increased. In this case there is increased protection against unstable operation and short-circuits, and the operation of converter-controlled motors even with large load peaks, is extremely reliable.

According to the invention the conductors of the additional winding are embedded in the pole shoes in an insulated manner.

The additional winding can be` so connected that for example when the supply comes from a direct-current network, the load current from the direct-current side passes through it. lt is however suificient when by means of a shunt only part of this current passes to the winding. When alternating or three-phase current is used, a different arrangement is employed depending upon whether an intermediate direct-current circuit is provided or not. ln the former case the current in the intermediate circuit ows through the additional winding or part of it, whilst in the latter case however the current has to be taken from the alternating current side in order to achieve dependence on the load. Current transformers are then provided which are connected to the additional winding by means of rectiers. These current transformers can be located either in the circuit of the alternating current supply system or directly in the main current circuit of the motor after the converter set. In the latter case care must be taken to ensure that the transformation of the current transformers is as far as possible independent of the frequency.

Fig. 1 is a generic diagrammatic illustration of my invention;

Fig. 2 is an electrical schematic diagram of the invention as utilized in an embodiment where the converter motor is fed from a direct-current supply;

Fig. 3 is a schematic diagram of the invention as utilized in an embodiment where the converter motor is fed from an A.C. supply; and

Fig. 4 is a schematic diagram of a second embodiment of the invention where the converter motor is fed from an A.C. supply.

In Fig. l reference numeral 1 indicates the field magnet which carries the excitation winding and 2 are the armature windings of the stator. in this example it is assumed that the excitation winding rotates with the eld poles and the armature is stationary. The opposite arrangement can of course also be employed. The armature bars through which the main current ows are indicated by 2a to 2f. The current flow of neighbouring conductors is displaced by 60. With the relative position of the armature and field magnet shown in the drawing, 2a and 2d correspond to the phase position of phase v, 2b and 2e to that of u, and 2c and 2f to that of w. At the indicated instant, current flows in u (2b) in a direction perpendicular to the plane of the paper from the rear to the front, this being indicated by the encircled dot which is the tip of the arrow for showing the direction of the current. This current flows in the opposite direction in bar 2e, this being indicated by the encircled cross for the arrow going in the opposite direction, and it flows back again in phase v as can beseen in Fig. 1. The current in bar 2d thus flows from the front to the rear and in 2a from the rear to the front. Bars 2c and 2f are without current at this instant. The excitation winding supplied with direct current is` designated by 3. and the direction of flow is also indicated. 'Thisy winding surrounds the poles. ofy the field magnet in a known manner. The additional winding 4 according to the in. vention is embedded in the4 pole shoes. The current flows through this winding from front to rear at the north pole and from rear to front at the south pole. It will be noted that the direction of the current and thus the ux is opposed to the armature current and thus the effect of they latter can. either be weakened, compensated or reversed, depending uponthe strength of the current.

always remains the same independently of the load.

Fig. 2 shovvs an-` arrangement where the converter motor 5 is fed from a direct-current system 6.v Reference number 7 indicates the inverters whose ignition is controlled by the control device 8 and the auxiliary direct voltage 10. The armature windings of the motor are indicated by 2 andthe excitation winding by 3. Reference number 4 indicates the additional. windingA which in accordance with` the invention effects the improvement inr the., ignition by compensating the armature reaction. It is located directly in the direct-current circuit supplying the inverters.

In Fig. 3 the converter motor is supplied from an alternating current network. Thecontrol device` is not shown and only` the armature and excitation circuitA are illustrated. The alternating current is for instance represented by the star-connected secondary winding 11 of an alternating, current transformer. The rctiers 12 rectify the alternating current and supply it to the inverter arrangement. The additional Winding in this case lies in the intermediate direct-current circuit.

In the embodiment illustrated in Fig. 4 the A.C. supp,ly voltage,r 11 is fed directly through the inverter unit 7 to the armaturewindings 2. The excitation Winding 3 is supplied by the excitation voltage source 9. A threephase voltage is tapped off from the A.C. supply voltage by means of the transformers 1-3 and is rectied by means of the rectifiers 14. This rectified-voltage, which isthusl a function of the load current, is then supplied to the additional winding 4 in accordance with my invention.

While in accordance with the provisions of the statutes I have illustrated and described the best form of embodi- The` curr-.ent` iiowing in this additional windingy is proportional to.. the load current, so that the: effect 1. ments of my invention known to me, it will be apparent to those skilled in the art that changes may be made in the form of the invention described without departing from the spirit of my invention as set forth in the appended claims.

I claim:

1. In a commutatorless converter motor having an excitation circuit' including field poles excited by direct current and an armature circuit including armature conductors, means for opposing the armature reactioncaused by the load current in the armature circuit comprising an auxiliary winding in the excitation. circuit supplie-d by a direct-current proportional to the load current, said auxiliary winding being arranged with respect to the field poles to develop a magnetic flux having an axis displaced with respect to that of the main field.

2. A commutatorless converter motor as defined in claim 1 wherein the conductors of the auxiliary winding are insulated and are embedded in the pole shoes of field poles of opposite polarity.

3. A commutatorless converter motor as defined in claim 2 wherein the direction of current travel through the conductors of the auxiliary winding is opposite to the direction of cur-rent travel through adjacent conductor bars of the armature winding arranged-generally parallel with respect to the auxiliary winding bars.

4. A commutatorless converter'motor as defined in claim l, wherein the armature circuit is supplied byalternating current from an inverter network fed from a direct-current source, and said auxiliary winding is connected in series with said inverter netwerk tofsaid direct-current source.

5. A commutatorless converter motor as defined in claim 1, wherein the armature circuit is supplied byy alternating current from an inverter network fedI from a rectified alternating-current source, and. said auxiliar-y winding is connected in series with the inverter network to said rectified alternating-current source.

6. A commutatorless converter motor as defined in claim 1 wherein the armature circuitv is supplied by alternating current from an inverter network fed from a rectified alternating-current source, and said auxiliary winding is fed through rectiers from current transformers connected t0 said alternating-current source.

References Cited in the file. of this patent UNITED STATES PATENTS 2,015,745 Deri Oct. 1, 1935 2,023,255 Stohr Dec. 3, 1935 2,085,109 Ludwig June 29,l 1937